It is well known in the art that when titanium dioxide is exposed to light, a photocatalytic reaction takes place, and such reaction is able to decompose volatile organic compounds or other gaseous pollutants. Thus, photocatalyst is frequently applied to air purification system in order to remove gaseous pollutants, and improve indoor air quality.
In building circulating systems, pollutants from various sources contribute to indoor air pollution, which poses a significant risk towards human health. Illnesses resulting from such indoor pollutants are generally known as the “sick building syndrome.” Therefore, in many heating, ventilation, and air conditioning (HVAC) systems, air purification systems are installed so as to remove air pollutants. Particularly, photocatalytic air purification systems are frequently used.
US2004/0238344 discloses an air purification system using excimer lamps for ultra-violet photocatalytic oxidation, and such air purification system can be used in HVAC system. Comparing to conventional low-pressure mercury lamps, the excimer lamps can provide UV radiation with desirable range of wavelength, thereby increasing the efficiency of the photocatalytic reaction. However, the implementation of the excimer lamps increases substantially the cost of the system.
US2011/0150720 provides an air filtration system and a method for making a photocatalytic oxidation substrate by coating a photocatalyst onto a metal substrate. However, the amount of the photocatalyst coated on the metal substrate is limited, resulting in low air pollutant removal efficiency.
US2013/0052113 relates to a method and a device for the purification of air by passing a flow of the air through a filter having a photocatalytic action subjected to UV lighting. The filter comprises a felt of mineral fibers, the fibers of which are coated with a material having a photocatalytic action, the residence time of the air in contact with the filter is greater than 70 msec and the UV lighting has a power of less than 35 mW per cm2 of lit surface of filter having a photocatalytic action. Nevertheless, the felt induces high air resistance, leading to high loading of the air flow generation unit.
According to an example in a prior art, FIG. 1 shows a cylindrical metal substrate coated with photocatalyst of an air purification unit. An UV lamp is installed along the axis of the metal substrate. The holes on the metal substrate are used for allowing air to pass through. Nevertheless, the performance of air pollutant removal is not effective since only limited amount of photocatalyst is coated on the metal substrate.
Consequently, there is an unmet need for a photocatalytic air purification system that can generate efficient air pollutant removal rate with minimal air resistance.